Systems and methods for balancing multi-cell batteries with a transformer and a rectifier circuit

Abstract

Systems and methods for balancing multi-cell batteries are provided. In one embodiment, the battery balancing circuit includes a battery including a plurality of cells coupled in series, a first terminal and a second terminal, a transformer including a primary winding and a plurality of secondary windings, where each secondary winding is coupled to one of the plurality of cells via a secondary switch and a rectifier circuit, where the primary winding is coupled between the first terminal and the second terminal of the battery, a primary switch in series with the primary winding of the transformer, and a control circuitry coupled to the primary switch, the plurality of secondary switches, and each of the plurality of cells.

What is claimed is: 
     
         1 . A battery balancing circuit comprising:
 a battery comprising a plurality of cells coupled in series, a first terminal and a second terminal;   a transformer comprising a primary winding and a plurality of secondary windings, wherein each secondary winding is coupled to one of the plurality of cells via a secondary switch of a plurality of secondary switches and a rectifier circuit, wherein a center-tap terminal of the primary winding is coupled to the first terminal of the battery;   a first primary switch coupled in series between a first terminal of the primary winding and the second terminal of the battery;   a second primary switch coupled in series between a second terminal of the primary winding and the second terminal of the battery; and   a control circuitry coupled to the first primary switch, the second primary switch, the plurality of secondary switches, and each of the plurality of cells, the control circuitry being configured to:   identify a subset of the plurality of cells exhibiting an imbalance condition;   identify remaining ones of the plurality of cells other than the subset of the plurality of cells;   close a subset of the plurality of secondary switches coupled to the identified subset of the plurality of cells and open remaining ones of the plurality of secondary switches coupled to the identified remaining ones of the plurality of cells; and   repeatedly open and close the first and second primary switches while the subset of the plurality of secondary switches are closed and the remaining ones of the plurality of secondary switches are opened.   
     
     
         2 . The circuit of  claim 1 , wherein the control circuitry is configured to identify the subset of the plurality of cells by measuring a voltage at each of the plurality of cells and comparing the measured voltage at each of the plurality of cells with a preselected threshold,
 wherein the control circuitry is further configured to transfer energy from the battery to the subset of the plurality of cells.   
     
     
         3 . The circuit of  claim 2 , wherein the control circuitry is configured to actuate the first primary switch and second primary switch at a preselected frequency and with a preselected duty cycle. 
     
     
         4 . The circuit of  claim 2 , wherein the imbalance condition is selected from the group consisting of an under-voltage and an over-voltage. 
     
     
         5 . The circuit of  claim 1 , wherein a first control line is coupled between the control circuitry and the first primary switch and wherein an inverter is coupled between the first control line and the second primary switch. 
     
     
         6 . The circuit of  claim 1 , wherein the control circuitry is configured to:
 detect a level of charge in each of the plurality of cells;   energize the primary winding by switching the first primary switch and the second primary switch; and   provide a path for energy from the primary winding to the identified subset of the plurality of cells by switching subset of the plurality of secondary switches.   
     
     
         7 . The circuit of  claim 1 , wherein each of the rectifier circuits comprises a full wave rectifier. 
     
     
         8 . The circuit of  claim 7 , wherein the full wave rectifier comprises a center tapped full wave rectifier comprising at least two diodes. 
     
     
         9 . The circuit of  claim 1 , wherein each secondary winding is connected to a corresponding rectifier circuit and a corresponding secondary switch is connected between the corresponding rectifier circuit and a corresponding cell of the battery. 
     
     
         10 . The circuit of  claim 1 , wherein each of the rectifier circuits consists of a diode.